Certain arc discharge devices, such as high pressure sodium lamps, employ ceramic discharge tubes. These tubes generally comprise an elongated, tubular body of, for example, polycrystalline alumina, which have electrodes sealed into the ends thereof. The electrodes are mounted in disks of the same material as the arc tube. The disks have an outside diameter sized to fit within the inside diameter of the body with enough clearance to allow for the presence of a sealing material, such as a high temperature frit. The positioning of the electrode along the longitudinal axis of the device is usually accomplished by means of a wire stop which is secured to the electrode. A similar wire stop is used to position the disk and hold it in the proper position with the body for sealing. There are many problems with this type of seal. The disk itself can cock during the sealing operation which provides a poor seal and an off-center electrode. Two wire stops are used to support the disk and the electrode. Further, even though extremely tight tolerances are maintained on the arc tube inside diameter and the disk outside diameter, there is no convenient way to center the disk in order to provide the proper seal annulus. This annulus is critical for seal integrity.